HIV is a retrovirus that causes immunosuppression in humans, and leads to a disease complex known as acquired immunodeficiency syndrome (AIDS). HIV disease is characterized by progressive functional deterioration of the immune system. The treatment of HIV disease has been significantly advanced by the recognition that combining different drugs with specific activities against different biochemical functions of the virus can help reduce the rapid development of drug resistant viruses that were seen in response to single drug treatment. However, even with combined treatments, multi-drug resistant strains of the virus have emerged. There is therefore a continuing need for the development of new anti-retroviral drugs that act specifically at different steps of the viral infection and replication cycle.
The integrase (IN) enzyme is an example of such a specific target. This enzyme catalyzes the insertion by virally-encoded integrase of proviral DNA into the host cell genome, which is the mechanism by which HIV and other retroviruses are introduced into human T-lymphoid cells. For HIV-1, this process is mediated by a 32 kD virally encoded integrase, having conserved sequences in the HIV long terminal repeats (LTR). Integration is believed to be mediated by integrase in three steps. The first, assembly, produces a stable nucleoprotein complex with viral DNA sequences via reverse-transcription in the cytoplasm of infected cells. Integrase then cleaves two nucleotides from each of the 3′ termini of the linear viral DNA ends which contain a highly conserved CA motif. The third step, strand transfer, involves covalently joining the recessed 3′ OH termini of the viral DNA at a staggered cut made at the host target site. The cleaved DNA migrates to the nucleus as a part of a large nucleoprotein complex, where the integrase catalyzes the insertion of viral DNA into a host chromosome by a direct transesterification reaction.
In vitro assays have previously been developed to identify integrase inhibitors (see, e.g., Mazumder et al. “Retroviral Integrase: A Novel Target in Antiviral Development; Basic In Vitro Assays with the Purified Enzyme,” in: Antiviral Methods and Protocols, Kinchington et al., Ed.; The Humana Press, Inc.: Totowa, N.J., 1999, pp. 327-335; Marchand et al., “In vitro human immunodeficiency virus type I integrase assays,” Methods Enzymol. 340: 624-633, 2001; and Chow, S. A., “In vitro assays for activities of retroviral integrase,” Methods 12:306-17, 1997), and have permitted the discovery of diverse classes of drugs that inhibit integrase (see, e.g., Pommier et al., “HIV-1 integrase as a target for antiviral drugs,” Antiviral Chem Chemother 8:483-503, 1997; Neamati et al., “Design and discovery of HIV-1 integrase inhibitors,” Drug Discovery Today 2:487-498, 1997). However, the drugs discovered by these assays have not been highly selective and potent inhibitors of the integrase enzyme. Many of these drugs have additionally been non-selective inhibitors of reverse transcriptase or HIV protease, which limits their usefulness in combination therapy directed to different specific steps of the retroviral life cycle. Moreover, a significant number of patients fail to respond to treatments with reverse transcriptase or HIV protease inhibitors, and viral resistance remains a major problem. Hence, there exists a need for integrase inhibitors that can be useful for acquired immune deficiency syndrome (AIDS) therapy.